'The Mediterranean Blue' Diamond Lives Up to Pre-Auction Hype, Fetches $21MM

The 10.03-carat “Mediterranean Blue” lived up to its pre-auction hype at Sotheby’s Geneva on Tuesday, selling for an impressive $21.3 million following a fast-paced, live-streamed bidding war.

Introduced as Lot 602 at 6:50 p.m. local time (12:50 p.m. EST), the Fancy Vivid Blue diamond headlined the evening sale. Two phone bidders engaged in a spirited three-minute exchange that included 13 individual offers.

Bidding opened at 9 million Swiss francs (approximately $10 million) and advanced rapidly in increments of 500,000 francs. At the 14 million franc mark, the pace slowed, with bids increasing by 200,000 to 300,000 francs before auctioneer Quig Bruning brought down the hammer at 15 million francs (about $17.9 million).

Including buyer’s premium and fees, the final price came to 17.86 million Swiss francs—equivalent to $21.3 million, or $2.12 million per carat. The identity of the winning bidder has not been disclosed.

Ahead of the sale, Sotheby’s spotlighted The Mediterranean Blue for its exquisite cushion shape, exceptional size, clarity, and vivid saturation. With a pre-sale estimate of $20 million, the house positioned the stone alongside the world’s most iconic blue diamonds.

That elite list includes the 15.1-carat “De Beers Cullinan Blue” ($57.5 million, Sotheby’s Hong Kong, 2022), the 14.6-carat “Oppenheimer Blue” ($57.5 million, Christie’s Geneva, 2016), and the 12.03-carat “Blue Moon of Josephine” ($48.5 million, Sotheby’s Geneva, 2015).

“The Mediterranean Blue represents one of nature’s rarest gems,” said Bruning, Head of Jewelry for Sotheby’s Americas & EMEA. “Any vivid blue diamond is a discovery worth celebrating, but one as entrancing as this—especially over 10 carats—is a newsworthy event.”

In its Monograph, the Gemological Institute of America (GIA) described The Mediterranean Blue as “a complete indulgence of the senses.”

The diamond received the highest possible color grading for a blue diamond from the GIA and was classified as Type IIb—a category that represents less than 0.5% of all diamonds.

The Mediterranean Blue was cut from a 31.94-carat rough diamond unearthed in 2023 at South Africa’s famed Cullinan Mine. Following a meticulous six-month planning and cutting process, the stone was transformed into a cushion modified brilliant.

Blue diamonds owe their remarkable hue to trace amounts of boron within the diamond’s carbon lattice. Scientists believe they form at extreme depths—around 400 miles below the Earth’s surface—approximately four times deeper than most other diamonds.

Credits: Images courtesy of Sotheby’s; screenshot via sothebys.com.